Slag treatment material

ABSTRACT

A method for improving the characteristics of fused slag material is disclosed. This improved method results in a fused slag having resistance against pulverization at the cooling process for generation of yellowish turbid water due to contact of slag lumps with rain water, this method characterized by forming a slag treatment material by rough crushing a substantially dehydrated heat-treated material containing boron, and adding that slag treatment material to molten slag.

This is a continuation in part of application Ser. No. 226,278, filedJul. 29, 1988 now abandoned.

BACKGROUND OF THE INVENTION

1. Industrial Field of the Invention

This invention relates to a slag treatment material for modifying theproperties of iron slag and steel slag, and, more particularly, to animproved slag treatment material which can effectively act to prevent,when a cooling process is applied to such iron slag or steel slag asblast furnace slag, the powdering of the slag due to disintegration ofthe generation of yellowish turbid water when slag lumps come intocontact with water.

2. Prior Art

A steel slag, particularly stainless steel slag, which has a basicity(weight ratio CaO/SiO₂) of substantially 1.5 or more, has a propertywhereby the 2CaO.SiO₂, phase changes from an α-type phase to an α'-typephase, and then changes to a γ-type phase or β-type phase when the slagis subjected to a cooling process. In many cases, when the slag changesfrom the α'-type phase to the γ-type phase, a volume expansion ofsubstantially 14% results. As it well known, this causes the slag topowder into fine particles.

This powdering phenomenon worsens the working environment, and disturbsfurther utilization of slag. Present stainless steel manufacturers aretherefore faced with serious problems in regard to the treatment ofslag.

It has long been a problem for stainless steel manufacturers to find amethod of preventing the powdering of slag and of solidifying it sincethe discharged slag can be effectively utilized as a secondary materialin such applications as engineering aggregates for road construction andso on.

Known methods of preventing the powdering of slag can be exemplified asfollows:

1 a method in which slag is made into water-granulated glass when theresidue slag is discharged;

2 a method in which slag is modified to form a material which mainlycomprises (CaO.SiO₂ and has a basicity of 1.5 or less (in practice thiscan be slightly varied according to the composition of the slag);

3 a method in which the phase change from an α'-type phase to a γ-typewhich results in a great change in density is controlled and the phasechange from an α'-type phase to a β-type phase is activated.

However, in regard to 1, at the time of water granulation, a phreaticexplosion can occur due to the presence of molten metals carried at thetime of discharge of the slag, and since water granulated glass is asoft material, it does not have sufficient strength to serve as anengineering aggregate. Therefore, this method 1 has not yet been putinto practical use although it has been partially tested.

In regard to 2, although some additives designed to modify theproperties of the SiO₂ containing material have already been placed onthe market, they require the installation of supplying facilities andstirring facilities since a large quantity of SiO₂ needs to be employedequivalent to substantially 20% of the molten slag. Furthermore, theslag viscosity is increased according to the drop in temperature of themolten slag following the addition, and this is not suitable from theviewpoint of workability and total cost.

The method 3, that is, bringing about a phase change from an α'-typephase to a β-type phase has been studied for many years and a variety ofmethods have been disclosed. One of these methods, which is the mosteffective and assured method available at present. [see Japanese PatentLaid-Open No.43690/1978 and the Kawatetsu Engineering Report Vol. 18,No. 1 (1986) 20 to 24] is one in which Si⁴⁺ ions are replaced by B₃₊ions having a smaller diameter than that of the Si⁴⁺ ions contained inthe slag.

However, the above-described conventional boron type of slag powderingpreventing material is in the form of fine powder and adehydration/vaporization reaction occurs at the time of contact with themolten slag since the boronic slag powdering preventing material is onecontaining water. As a result of this, a blowing phenomenon of the slagpowdering preventing material is generated, causing the workingenvironment to become excessively worsened and sometimes dangerous.Therefore operation of the work is very difficult.

Furthermore, since the conventional boron type of slag powderingpreventing material differs significantly in the chemical compositionand properties from slag, differences in viscosity and density from thefused slag can be easily generated, that is, the so-called affinitybetween the slag and the slag powdering preventing material is notsufficient and thereby the diffusing/mixing performance is insufficient.As a result of such disadvantages, the boron type of slag powderingpreventing material cannot be put into practical use although there havebeen some proposals therefor.

A second problem arises in such iron or steel slag as blast furnace slagin that so-called "yellowish turbid water" is generated when the slagcomes into contact with water such as rain or gutter water.

As is well known, blast furnace slag is widely used as variousaggregates, particularly as road beds. However, it has been confirmedthat if the percentage of sulfur contained in the slag is high, amistake in the conditions or methods for use will cause yellowish turbidwater and hydrogen sulfide smells to be generated due to rain water orgutter water which has been brought into contact with the slag.Particularly in order to ensure that the slag quality for roadconstruction is free from such problems, it is a rule that such slagshould not generate any yellowish turbid water or hydrogen sulfidesmells. In order to evaluate this fact, a color identification test isemployed, and slag should satisfy this test (JIS A 5015 made public onNov. 1).

The phenomenon of generation of yellowish turbid water is caused fromthe elution of sulfur (S) contained in the form of calcium sulfide (CaS)which is contained, as a major part, in slag, and is due to generationof yellow polysulfide (such as CaSx) after being applied to a hydrolysisprocess. Known methods of preventing generation of yellowish turbidwater can be exemplified as follows:

1 a method where slag is subjected to aging in which it is oxidized bywater and air until it is stabilized;

2 a method in which an oxidant is added to molten slag;

3 a method in which slag is treated with CO₂ so that the surface of theslag is stabilized; and

4 a method in which the cooling speed of slag is raised.

In regard to 1, aging treatment takes almost one to three months to becompleted, requiring the use of a very broad space (slag yard) forstorage.

In regard to 2, several methods can be exemplified such as a method inwhich a high degree of ferrous oxide is added or a method in which a gascontaining oxygen, such as air, is added. However, this method is notpreferable since poisonous SO₂ gas is generated due to the reaction.Furthermore, with this method, the generation of the yellowish turbidwater cannot be sufficiently prevented.

In regard to 3, although the surface of slag can be stabilized, when itis used as ballast this method is disadvantageous in that fused sulfidescan again overflow from the fractured surface when it is crushed.

The method 4 is a method in which glass is prepared by degrading,diffusing and rapidly cooling down fused slag so that the includedsulfur component is prevented from oozing out. However, this involvessuch problems as a deterioration in strength and necessitatesgranulation to below a specific viscosity to form the glass, allowing itto be used as a material for thin aggregates, but making it verydifficult to be used as rough aggregates.

Although other methods have been disclosed in which iron, manganese orzinc is, as an effective component, added so that sulfides are fixed,these methods have not been put into practical use due to high costs andinsufficient effects.

Therefore, at present, the method 1 in which slag is subjected to agingis the only available method for preventing generation of yellowishturbid water from slag.

Problems to be Solved by the Invention

As can be clearly seen from the above description, this invention isintended to overcome the long time problems of powdering and generationof yellowish turbid water from iron and steel slag by means of anindustrially low-cost and convenient slag treatment material.

Therefore, an object of the present invention is collectively toovercome the problems by improving the conventional boron type ofpowdering prevention material so that the reaction in which Si⁴⁺ isreplaced by B³⁺ is further effectively accelerated for the purpose ofmodifying the properties of slag.

SUMMARY OF THE INVENTION

The inventors of the present invention therefore have investigatedimproving boron type of slag powdering prevention materials to completethe present invention.

That is, this invention relates to a slag treatment material whichmodifies properties of iron slag that has resistance against slagpowdering during the process of cooling molten slag and againstgeneration of yellowish turbid water when slag is brought into contactwith rain water. The treatment material for improving the properties ofiron slab is characterized in that it comprises a material obtained bycoarsely crushing a substantially dehydrated heat-treated materialcontaining boron.

DETAILED DESCRIPTION OF THE INVENTION Operation

The operation of the present invention will now be described.

The characteristics of the slag treatment material according to thepresent invention, different from conventionally known crystal hydratedborate powders used to prevent powdering in steel and iron slag, lie inthat it comprises a material which is obtained by coarsely crushing asubstantially dehydrated heat-treated material (hereinafter referred toas "heat-treated material containing boron"). The affinity of theheat-treated material containing boron of the present invention tomolten slag mainly composed of basic calcium silicate (simply termed"slag" hereinafter) occurring in steel or iron making or the like, issuperior to a material containing crystal hydrated borate, the precursorof the former. The result in uniformity with slag favorably surpassedthe expectations of the inventors of the present invention.

In this case, the heat-treated material containing boron preferablycontains a relatively high percentage of boron, it being contained, inmany cases, at about 10 wt % or more B₂ O₃ m preferably about 20 wt % ormore.

As a material of the type described above, the following material whichhas been heat treated can be exemplified:

materials mainly containing two-component type borates such as naturalor synthetic alkali borate, alkaline earth metal borate, borosilicate;

materials mainly containing three-component type borosilicates such asalkali borosilicate, alkaline earth metal borosilicate;

materials mainly containing alumino-borosilicates; or

materials mainly containing the four components of boron, silicone, analkali metal and an alkaline earth metal.

Heat-treated material containing boron refers to material containing atleast 80 wt % of the above-described main component, in which case theabove-described main component contains at least 10 wt % as B₂ O₃, orpreferably 20 wt % as the effective component.

Therefore, remaining components may comprise at most 20 wt %, suchcomponents being exemplified by materials unavoidably involved in mixingduring the preparation of the heat-treated material, materials foradjusting properties such as melting points, softening points,viscosities, surface tensions, or materials which can be fixed assulfides.

Such components can be exemplified by Na₂ O, K₂ O, Li₂ O, CaO, MgO, BaO,SiO₂, Fe₂ O₃, Al₂ O₃, MnO₂, ZnO, P₂ O₅, CaF₂ or materials containingthese components.

In the above-described materials those containing alkali metal boratesas the major component, are from a practical view point preferablyrepresented by the following general formula: Me₂ O.nB₂ O₃ (wherein Merepresents one or two or more types of alkali metal elements selectedfrom Li, K and Na, and n represents the range of the number of molesbetween 1 and 10). Those containing alkaline earth metal borates as themajor component are preferably represented by the following formula:MeO.nB₂ O₃ (wherein Me represents one or two or more alkaline earthmetal elements, n represents the range of the number of moles between 1and 5). Those containing borosilicates are preferably represented by thefollowing general formula: SiO₂.nB₂ O₃ (wherein n represents the numberof moles between 1 and 9). Those containing borosilicates are preferablyin the range where B₂ O₃ : 10 to 80 wt %, SiO₂ : 5 to 70 wt %, Me₂ O:2to 50 wt % (however, B₂ O₃ +SiO₂ +Me₂ O≧80 wt %) and the others: 0 to 20wt %. Those containing alkaline earth metal borosilicates are preferablyin the range where B₂ O₃ :20 to 80 wt %, SiO: 10 to 60 wt %, Me₂ O:5 to40 wt % (however B₂ O₃ +SiO₂ +Me₂ O≧80 wt. %) and the others: 0 to 20 wt%. Those containing alumino-borosilicates are preferably in the rangewhere B₂ O:20 to 60 wt %, SiO₂ :5 to 50 wt %, Al₂ O₃ :2 to 20 wt %, Me₂O:5 to 50 wt % (wherein Me represents an alkali metal or alkaline earthmetal, and n represents the valence), (however B₂ O₃₊ SiO₂ +Al₂ O₃+Me_(2/n) O≧80 wt %) and the others: 0 to 20 wt %. Those containing amaterial containing boron as the major component of the four componenttype preferably are in the range where B₂ O₃ :20 to 60 wt %, Si₂ :10 to50 wt %, Me₂ O:3 to 20 wt %, and MeO: 5 to 35 wt %.

The reason for the above lies in that all of the above-describedmaterials containing boron can be easily melted and diffused at thetemperature of the molten slag since then the melting points andsoftening points are in the range of about 1100° C. or less, preferablyin the range of 700° to 1050° C. so that the need for the heat treatedmaterial containing boron to be quickly melted and diffused in themolten slag can be satisfied due to its composition.

Heat-treated material containing boron here refers to a substantiallydehydrated heat treated material which is obtained by sintering orvitrifying a material containing a boron component as the majorcomponent. Therefore, sintered materials, glass materials and theirmixtures can be included in the heat-treated material containing boronand glass materials are particularly preferable for use in the presentinvention. Vitrification here refers to materials made amorphous to adegree where they cannot be clearly defined with a specific strength ofanalyzing rays when X-ray analysis is conducted.

The heat-treated material containing boron according to the presentinvention is crushed for use, however, this needs to be a material whichhas been coarsely crushed.

Therefore, although in many cases, the particle size distribution willrange from 0.1 mm or larger to fist sized lumps or cullets, a particledistribution where 0.1 to 50 mm particles are 90% or more of thedistribution is preferable.

The reason why coarsely crushed treatment material is required accordingto the present invention lies in that if particle size is 0.1 mm orless, condensation occurs between fine particles, preventing thematerial from being smoothly melted in the molten slag although thisdepends upon how it is added to the molten slag. Furthermore, non-meltedlumps will sometimes be generated, or a dust phenomenon will occur atthe time of addition in the furnace.

On the other hand, although large coarsely crushed treatment material ispreferable, in view of uniformly improved properties of slag arisingfrom the stirrings effect caused by the addition thereof to molten slag,if the lumps or cullets exceed fist size then unmelted portions will begenerated, a situation that needs to be avoided.

Therefore, a supplement can be, if necessary, mixed with theabove-described slag treatment material in order to improve the effectsfor quickly melting, diffusing and mixing with the molten slag after theslag treatment material has been added.

Such a supplement may be a powder in which dehydrating and/ordecarbonizing reactions are generated by applying heat. Powders of thetype described above can be exemplified by one or more of materialsselected from: aluminosilicates such as clay, activated clay,diatomaceous earth; other aluminosilicates such as bentonite, perliteand zeolite; carbonates or bicarbonates such as limestone, sodium,potassium, calcium, magnesium or barium carbonate; or borates such asborax, kernite, ulexite or colemanite.

Although the mount of addition of the above-described supplement differsaccording to type, method of adding the slag powdering prevention agentproperties and state of the molten slag, it may be up to 30 wt % withrespect to the slag powdering prevention agent, and is preferably in therange of from 5 to 15 wt %.

The particle size of this supplement is preferably smaller than that ofthe slag powdering prevention agent and its mean particle size ispreferably smaller than the lower limit of the slag powdering preventionagent.

The slag treatment material according to the present invention can beprepared by mixing a starting material which contains a boron componentas the effective component, and heating the thus-mixed material so as tosinter or melt it, followed by cooling and crushing.

The boron type starting material can be exemplified by artificialmaterials such as boric acid, sodium borate, natural materials such asborax colemanite (Ca₂ B₆ O₁₁.5-H₂ O), ulexite (NaCaB₅ O₅ O₉.8H₂ O),tincal (Na₂ B₄ O₇.10-H₂ O), and kernite (Na₂ B₄ O₇.4H₂ O). The alkalinematerial can be exemplified by caustic alkali, alkali carbonate andalkali bicarbonate and so on. The alkali earth metallic material can beexemplified by carbonate, hydroxide, and oxides of alkaline earth metal.The silicon material can be exemplified by silica sand quartz sand,diatom, synthetic silica, slag, clay and the like. Other materials canbe exemplified by Fe₂ O₃, Al₂ O₃, MnO₂, P₂ O₅, fluoride, or materialscontaining these materials.

The above-described starting materials are properly selected, mixed toachieve the above-described ratio, and supplied to a required fusingfurnace or a calcining furnace so as to be heated/fused or calcined.Next, the thus heat-treated material is subjected to particle sizeadjustment after it has been cooled down whereby a desired product canbe obtained.

Although there is no reason for limiting the heating conditions,temperatures must be those at which water of crystallization or adheredwater can be, of course, substantially dehydrated, at which theparticles of the material can be calcined with each other, and at whichthey can be fused. Since this temperature differs in accordance with thecomposition of the material, it may be determined so as to correspond tothe specific heat treatment apparatus.

When vitrification is conducted, the most practical and thereforepreferable, method of cooling down the fused liquid is tapping the fusedliquid while applying pressured water to granulate the slag, andrecovering it as sand-like glass. Another method is one in which thefused liquid to be tapped is placed on a belt conveyer and cooled bywater or air to be recovered as cullets.

Next, particle size is adjusted after conducting drying so as to removeadhered water. However, in the case of water-granulated material,particle size adjustment by crushing and screening is not necessarilyrequired since dried material per se can be made into product.Therefore, the particle size adjustment need only be conducted ifnecessary. Sintered material is subjected to particle size adjustmentwith a conventional crusher.

In this case, the above-described supplement can be mixed in if desired.

Slags to which the present invention is directed ar slags mainlycontaining basic type calcium silicates that tend to disintegrate orpowder when being cooled or subjected to aging, or types that tend togenerate yellowish turbid water when brought into contact with water.Such slags generally have a basicity (weight ratio CaO/SiO₂) of at least1.3, preferably within the range between 1.5 and 3.5 and can beexemplified by blast furnace slag, steel slag for such as stainlesssteel, or converter slag etc.

Although the amount of slag treatment material to be added with respectto the amount of slag differs in accordance with its composition andproperties and the composition etc. of the slag it must be at leastabout 0.15 wt % as B₂ O₃ for the purpose of either preventing slagpowdering or preventing generation of yellowish turbid water, and bepreferably 0.3 wt % or more in consideration of durability of modifiedslag.

The reason for this lies in that, if it is less than about 0.15 wt %, itis not sufficient to prevent generation of yellowish turbid water andoccurrence of powdering. On the other hand, there is no reason to definean upper limit. In many oases, it is naturally limited from theviewpoint of economy or affect on molten metal. Therefore, thepreferable range from the viewpoint of practical use is from 0.3 wt % to1.5 wt %.

Slag can be improved by using the slag treatment material according tothe present invention without any particular change in the operatingconditions of conventional blast furnaces and steel furnaces, and theslag treatment material can be added to molten slag in the presence ornon-presence of molten metal it can be understood that this will be veryadvantageous.

Therefore, when molten iron is delivered from a blast furnace togetherwith a slag through gutters the slag treatment material may be addedinto a slag accumulated on iron by a dam disposed in the gutter throughsupplying port being disposed at the desired position on the gutter.Alternatively, it may be added at the time of delivery together withmolten slag.

In the case of manufacturing stainless steel or the like, the slagtreatment material is added, similar to the above description, duringthe time the stainless steel is delivered from an electric fusingfurnace to a ladle o during time the molten slag is tapped into a slagpot from the ladle.

In this case, the manner of adding the slag treatment material to moltenslag is not particularly limited and need only satisfy the necessitythat the slag treatment material should be quickly melted and diffusedinto the molten slag.

For example, a method in which the slag treatment material is added asit is to molten slag in the presence or non presence of molten metal, isa method in which the same is added under air pressure, a method inwhich it is supplied as bagged or a method in which molten slag issupplied to a place where the slag treatment material has beenpreviously supplied can be employed.

If the slag treatment material is added in the presence of molten metal,the degree of affect on the mixture of boron into the molten metal, etc.can be substantially neglected. This makes application of the slagtreatment material according to the present invention particularlyadvantageous.

Therefore, the slag treatment material is added only into a slag tappedin a slag pot when the above-described affect of boron is expected, butin other cases, it is practical to add it to the slag in the presence ofmolten metal which has been maintained at high temperature since theviscosity of the molten slag is relatively small, allowing the meltingand diffusion of the slag treatment material to be conducted quickly, asa result of which, the improvement in properties of the slag can beuniformly conducted.

If there is a fear of the slag treatment material insufficiently meltingor diffusing due to an increase in the viscosity of the molten slag whenit is added to a slag pot, re-heating of the slag or addition of theabove-described supplement is, if necessary, required for the purpose ofassisting diffusion of the slag treatment material.

Therefore, it is substantially unnecessary to provide any specialdiffusion means for rapidly melting or diffusion of the slag treatmentmaterial after it has been added to the molten slag.

As a result, slag whose properties have been improved can be obtained bygradual or rapid cooling in a normal way after the above-describedaddition has been conducted.

Embodiments

The present invention will now be described with reference to thefollowing embodiments.

EXAMPLE 1 1 Preparation of slag treatment material sample

The material mixture whose composition (by weight) is as follows(Table 1) was melted in an electric furnace, the thus-obtained moltenglass was rappidly charged into water, and the thus-obtained glassmaterial was coarsely crushed. The coarsely crushed glass showed aparticle size distribution without exception where particle sizes of 5to 30 mm were 90% or more of the product.

                                      TABLE 1                                     __________________________________________________________________________    Sample        Boric                Quartz                                     No. Colemanite                                                                          Borax                                                                             acid                                                                              K.sub.2 CO.sub.3                                                                  Li.sub.2 CO.sub.3                                                                 Mg(OH).sub.2                                                                       BaCO.sub.3                                                                        sand                                                                              Alumina                                __________________________________________________________________________    1         100 72.3                                                            2             100 49.7                                                        3             100     26.4                                                    4   100       79.3        84                                                  5             100              94.3                                           6             100                                                             7             100                  12.6                                       8             100                  9.8                                        9         100                      7                                          10            100 88               41                                         11            100     71           160                                        12  100       4.2                  4.4                                        13            100         92       19                                         14            100              64  17                                         15  100       13.3                 62.6                                                                              16.8                                   16            100 32.6    80.4     34.0                                                                              11.2                                   17            100              43  79.4                                                                              11.2                                   __________________________________________________________________________

Note: Boric acid used was an anhydride. Potassium carbonate, lithiumcarbonate, magnesium hydroxide, barium carbonate and alumina used wereindustrial chemical grade. Colemanite was constituted by 45%-B₂ O₃,25%-CAO, 4%-SIO₂, 24%-Ignition loss and 2%-balance. Borax wasconstituted by 21.43%- Na₂ O, 48.21%-B₂ O₃ and 29.96%-Ignition loss,both the colemanite and borax being made in Turkey. Quartz sand used wasdried 98%-pure SiO₂ from Africa.

The major compositions of samples Nos. 1 to 8 are shown in the followingtable 2.

                  TABLE 2                                                         ______________________________________                                        Sample No.         Glass composition                                          ______________________________________                                        1                  Na.sub.2 O.5B.sub.2 O.sub.3                                2                  K.sub.2 O.4B.sub.2 O.sub.3                                 3                  Li.sub.2 O.4B.sub.2 O.sub.3                                4                  CaO.4B.sub.2 O.sub.3                                       5                  MgO.B.sub.2 O.sub.3                                        6                  BaO.3B.sub.2 O.sub.3                                       7                  SiO.sub.2.7B.sub.2 O.sub.3                                 8                  SiO.sub.2.9B.sub.2 O.sub.3                                 ______________________________________                                    

The outline of the chemical compositions (weight %) of samples Nos. 9 to17 obtained similarly are as follows:

                                      TABLE 3                                     __________________________________________________________________________    Chemical analysis of Glass Samples Nos. 9 to 17 (weight %)                    Sample No.                                                                          B.sub.2 O.sub.3                                                                  Na.sub.2 O                                                                        K.sub.2 O                                                                        Li.sub.2 O                                                                       CaO                                                                              MgO                                                                              BaO                                                                              SiO.sub.2                                                                        Al.sub.2 O.sub.3                                                                  Residue                                    __________________________________________________________________________     9    63 28                  9                                                10    50     30             20                                                11    35        10          55                                                12    59           29       10     2                                          13    55              35    10                                                14    60                 30 10                                                15    35           15       39 10  1                                          16    45     10       25    15 5                                              17    45                 15 35 5                                              __________________________________________________________________________

2 Slag modification test

When slag having basicity (CaO/SiO₂ =2.10) which is the first moltenslag tapped from an electric furnace for manufacturing stainless steel(capacity: 30 tons) was removed i.e., tapped from a ladle to a slag pot,30 Kg of each of the above slag treatment material test samples weresimultaneously supplied in 10 Kg vinyl bags. Next, after thethus-supplied slag was solidified by allowing it to stand at lowtemperature, the state of the slags were observed until the temperaturereached room temperature.

The test conditions are as follows:

                  TABLE 4                                                         ______________________________________                                                                       B.sub.2 O.sub.3                                     Sam-   Amount of Amount of                                                                              contained                                                                            Temperature                             Test ple    tapping   sample added                                                                           in slag                                                                              at tapping                              No.  No.    (t)       (kg/t slag)                                                                            (wt %) (°C.)                            ______________________________________                                         1    1     4.99      6.01     0.51   1443                                     2    2     4.77      6.29     0.47   1421                                     3    3     5.76      5.20     0.47   1420                                     4    4     5.00      6.00     0.50   1407                                     5    5     3.65      8.21     0.52   1432                                     6    6     3.68      8.16     0.47   1422                                     7    7     5.56      5.39     0.48   1442                                     8    8     5.48      5.48     0.50   1449                                     9    9     3.71      8.10     0.51   1432                                    10   10     3.26      9.20     0.46   1411                                    11   11     2.23      13.43    0.47   1418                                    12   12     3.38      8.87     0.52   1444                                    13   13     3.37      8.91     0.49   1406                                    14   14     3.46      8.67     0.52   1428                                    15   15     2.21      13.58    0.47   1430                                    16   16     2.81      10.67    0.48   1430                                    17   17     2.65      11.33    0.51   1441                                    18   --     4.12      0        0      1431                                    19   --     4.07      0        0      1406                                    20   --     3.99      0        0      1413                                    ______________________________________                                    

After addition of each slag treatment test sample, no dust or gases weregenerated in any test, such that such addition of slag treatment testsample could be conducted safely. When molten slag was supplied i.e.,tapped to the slag pot, excellent diffusion and mixing of the slagtreatment test samples were observed.

After allowing each test amount of slag to stand at room temperature forcooling after addition of slag treatment test samples, the state of theslags were observed. Test Nos. 1 to 17 showed no powdering ordegradation.

On the other hand, conventional slags of test nos. 18-20 to which noslag treatment materials were added decayed and powdered after beingcooled.

The outline of the analyzed value (weight %) of slag used in the test isas follows:

    ______________________________________                                        Test No.  CaO      SiO.sub.2  MgO   Al.sub.2 O.sub.3                          ______________________________________                                        1 to 20   48 to 55 22 to 28   9 to 13                                                                             9 to 15                                   ______________________________________                                    

In none of the tests, was dust generation observed due to supply of thetest samples, and the test samples instantaneously splashed and flowedon the molten slag. The state of the slags were observed after each slaghad been allowed to stand and cool to room temperature. No decay orpowdering phenomenon were observed it was found that an excellent effectcan be obtained by using 0.46 to 0.53 wt % of B₂ O₃.

EXAMPLE 2 1 Preparation of slag treatment material sample

A fused liquid having the same glass composition as those used assamples Nos. 1, 2 and 4 according to Example 1 was granulated withpressured water, and the resultant crushed glass product was dried. Thenthe slag treatment materials shown in Table 5 were prepared.

                  TABLE 5                                                         ______________________________________                                        Slag treatment                                                                            Glass                                                             material    composition Particle size                                         ______________________________________                                        18          Na.sub.2 O.5B.sub.2 O.sub.3                                                               In all of the samples,                                19          Li.sub.2 O.4B.sub.2 O.sub.3                                                               particles sized from 0.1                              20          K.sub.2 O.4B.sub.2 O.sub.3                                                                to 5 mm shared 90%                                    ______________________________________                                    

2 Slag modification test

When slag having basicity (CaO/SiO₂ =2.02) which is the first moltenslag tapped from an electric furnace for manufacturing stainless steel(capacity: 30 tons) was removed from a ladle to a slag pot, 30 Kg ofeach of the above slag treatment material test samples weresimultaneously supplied in 10 Kg vinyl bags. Next, after thethus-supplied slag was solidified by allowing it to stand at lowtemperature, the state of the slags were observed until the temperaturereached room temperature.

The test conditions are as follows:

                  TABLE 6                                                         ______________________________________                                                                       B.sub.2 O.sub.3                                     Sam-   Amount of Amount of                                                                              contained                                                                            Temperature                             Test ple    tapping   sample added                                                                           in slag                                                                              at tapping                              No.  No.    (t)       (kg/t slag)                                                                            (wt %) (°C.)                            ______________________________________                                        21   18     5.20      16.3     0.49   1436                                    22   19     5.53      16.3     0.49   1404                                    23   20     4.39      17.0     0.51   1419                                    24   --     5.49      --       --     1420                                    ______________________________________                                    

After addition of each test sample, no dust or gases were generated inany test, and addition work could be conducted safely. When molten slagwas supplied to the slag pot, excellent diffusion and mixing wereobserved.

After allowing each slag to stand at room temperature for cooling afterbeing tested, the state of the slags were observed. Test Nos. 21 to 23did not show any decay or powdering.

After allowing these slag lumps to stand outdoors for three months, nochange was observed.

On the other hand, the conventional slag of test No. 24 to which no slagtreatment material was added decayed and powdered when it was cooled.

Comparative Example

In Example 2, borax (Na₂ B₄ O₇.10H₂)(B₂ O₃ :37.00 wt %, Na₂ O:16.5 wt%)(particles sized from 0.2 to 0.4. mm comprising 55%) of 12 kg/ton slagwas supplied in separate vinyl bags. Intense splash and blow resultedand un-dissolved lumps were generated, causing the supply to be stopped.

EXAMPLE 3 1 Preparation of slag treatment material sample

A fused liquid having the same composition as those used in the testsamples 4, 5 and 6 according to Example 1 was granulated with pressuredwater, and the resultant crushed vitrified product was dried. Then, theslag treatment materials shown in Table 7 were prepared.

                  TABLE 7                                                         ______________________________________                                        Sample   Glass                                                                No.      composition Particle size                                            ______________________________________                                        21       MgO.B.sub.2 O.sub.3                                                                       In all of the samples, particles                         22       CaO.4B.sub.2 O.sub.3                                                                      sized from 0.1 to 5 mm shared                            23       BaO.3B.sub.2 O.sub.3                                                                      90%                                                      ______________________________________                                    

2 Slag modification test

When slag having basicity (CaO/SiO₂ =2.06) which is the first moltenslag tapped from an electric furnace for manufacturing stainless steel(capacity: 30 tons) was removed from a ladle to a slag pot, 40 Kg ofeach of the above slag treatment material test samples weresimultaneously supplied in 10 Kg vinyl bags. Next, after thethus-supplied slag was solidified by allowing it to stand at lowtemperature, the state of the slags were observed until the temperaturereached room temperature.

The test conditions are as follows:

                  TABLE 8                                                         ______________________________________                                                                       B.sub.2 O.sub.3                                     Sam-   Amount of Amount of                                                                              contained                                                                            Temperature                             Test ple    tapping   sample added                                                                           in slag                                                                              at tapping                              No.  No.    (t)       (kg/t slag)                                                                            (wt %) (°C.)                            ______________________________________                                        25   21     5.28      7.58     0.48   1421                                    26   22     6.80      5.88     0.49   1441                                    27   23     4.91      8.15     0.47   1418                                    28   --     5.54      0        0      1427                                    ______________________________________                                    

After addition of each test sample, no dust or gases were generated inany test, and additional work could be conducted safely. When moltenslag was supplied to the slag pot, excellent diffusion and mixing wereobserved.

After allowing each slag to stand at room temperature for cooling afterbeing tested, the state of the slags were observed. Test Nos. 25 to 27did not show any decay or powdering.

After allowing these slag lumps to stand outdoors for three months, nochange was observed.

On the other hand, the conventional slag of test No. 28 to which no slagtreatment material was added decayed and powdered when it was cooled.

EXAMPLE 4 1 Preparation to slag treatment material sample

A fused liquid having the same composition as those used in the testsamples 7 and 8 according to the Example 1 was granulated with pressuredwater, and the resultant crushed glass product was dried. Then, the slagtreatment materials shown in Table 9 were prepared.

                  TABLE 9                                                         ______________________________________                                        Sample Glass                                                                  No.    composition                                                                              Particle size                                               ______________________________________                                        24     SiO.sub.2.7B.sub.2 O.sub.3                                                               In all of the samples, particles                            25     SiO.sub.2.9B.sub.2 O.sub.3                                                               sized from 0.1 mm to 5 mm shared 90%                        ______________________________________                                    

2 Slag modification test

When slag having basicity (CaO/SiO₂ =2.13) which is the first moltenslag tapped from an electric furnace for manufacturing stainless steel(capacity: 30 tons) was removed from a ladle to a slag pot, 30 Kg ofeach of the above slag treatment material test samples weresimultaneously supplied in 10 Kg vinyl bags. Next, after thethus-supplied slag was solidified by allowing it to stand at lowtemperature, the state of the slags were observed until the temperaturereached room temperature.

The test conditions are as follows

                  TABLE 10                                                        ______________________________________                                                                       B.sub.2 O.sub.3                                     Sam-   Amount of Amount of                                                                              contained                                                                            Temperature                             Test ple    tapping   sample added                                                                           in slag                                                                              at tapping                              No.  No.    (t)       (kg/t slag)                                                                            (wt %) (°C.)                            ______________________________________                                        29   24     5.68      5.28     0.47   1415                                    30   25     5.37      5.59     0.51   1445                                    31   --     5.20      0        0      1432                                    ______________________________________                                    

After addition of each test sample, no dust or gases were generated inany test, and additional work could be conducted safely. When moltenslag was supplied to the slag pot, excellent diffusion and mixing wereobserved. After allowing each slag to stand at room temperature forcooling after being tested, the state of the slags were observed. TestNos. 29 to 30 showed no powdering or degradation.

After allowing these slag lumps to stand outdoor for three months, nochange was observed.

On the other hand, the conventional slag of Test No. 31 to which no slagtreatment material was added decayed and powdered when it was cooled.

EXAMPLE 5 1 Preparation of slag treatment material sample

A fused liquid having the same composition as those used in thataccording to the Example 1 was fused in an electric furnace, granulatedwith pressured water, and the resultant slag treatment material shown inTable 11 was prepared.

                  TABLE 11                                                        ______________________________________                                        Sample  Composition (wt %)                                                    No.     B.sub.2 O.sub.3                                                                         Li.sub.2 O                                                                           Na.sub.2 O                                                                             K.sub.2 O                                                                          SiO.sub.2                              ______________________________________                                        26      34               15            51                                     27      63               28             9                                     28      30                        15   55                                     29      50                        30   20                                     30      35        10                   55                                     ______________________________________                                    

2 Slag modification test

When slag having basicity (CaO/SiO₂ =2.15) which is the first moltenslag tapped from an electric furnace for manufacturing stainless steel(capacity: 30 tons) was removed from a ladle to a slag pot, 50 Kg ofeach of the above slag treatment material test samples weresimultaneously supplied in 10 Kg vinyl bags. Next, after thethus-supplied slag was solidified by allowing it to stand at lowtemperature, the state of the slag were observed until the temperaturereached room temperature.

The test conditions are as follows:

                  TABLE 12                                                        ______________________________________                                                                       B.sub.2 O.sub.3                                     Sam-   Amount of Amount of                                                                              contained                                                                            Temperature                             Test ple    tapping   sample added                                                                           in slag                                                                              at tapping                              No.  No.    (t)       (kg/t slag)                                                                            (wt %) (°C.)                            ______________________________________                                        32   26     3.27      15.29    0.52   1407                                    33   27     6.30      7.94     0.50   1432                                    34   28     3.19      15.67    0.47   1423                                    35   29     4.90      10.20    0.51   1416                                    36   30     3.65      13.70    0.48   1440                                    37   --     5.22      0        0      1431                                    ______________________________________                                    

After addition of each test sample, no dust or gases were generated inany test and additional work could be conducted safely. When molten slagwas supplied to the slag pot, excellent diffusion and mixing wereobserved.

After allowing each slag to stand at room temperature for cooling afterbeing tested, the state of the slags were observed. Test No. 32 to 36showed no powdering or degradation.

After allowing these slag lumps to stand outdoor for three months, nochange was observed.

On the other hand the conventional slag to which no slag treatmentmaterial was added decayed and powdered when it was cooled.

EXAMPLE 6 1 Preparation of slag treatment material sample

A fused liquid having the same composition as that used in Example 1 wasfused in an electric furnace, granulated with water, and the resultantslag treatment material shown in Table 13 was prepared.

                  TABLE 13                                                        ______________________________________                                        Sample  Composition (wt %)                                                    No.     B.sub.2 O.sub.3                                                                      CaO      MgO  BaO    SiO.sub.2                                                                          Na.sub.2 O                           ______________________________________                                        31      59     29                   10                                        32      40     30                   25   5                                    33      55              30          10                                        34      30              15          50   5                                    35      60                   30     10                                        36      25                   20     44   11                                   ______________________________________                                    

2 Slag modification test

When slag having basicity (CaO/SiO₂ =2.10) which is the first moltenslag tapped from an electric furnace for manufacturing stainless steel(capacity: 30 tons) was removed from a ladle to a slag pot, 40 Kg ofeach of the above slag treatment material test samples weresimultaneously supplied in 10 Kg vinyl bags. Next after thethus-supplied slag was solidified by allowing it to stand at lowtemperature, state of the slags were observed until the temperaturereached room temperature.

The test conditions are a follows:

                  TABLE 14                                                        ______________________________________                                                                       B.sub.2 O.sub.3                                     Sam-   Amount of Amount of                                                                              contained                                                                            Temperature                             Test ple    tapping   sample added                                                                           in slag                                                                              at tapping                              No.  No.    (t)       (kg/t slag)                                                                            (wt %) (°C.)                            ______________________________________                                        38   31     4.78      8.37     0.49   1415                                    39   32     3.40      11.76    0.47   1442                                    40   33     4.31      9.28     0.51   1430                                    41   34     2.61      15.33    0.46   1431                                    42   35     4.90      8.16     0.49   1439                                    43   36     2.22      18.02    0.45   1420                                    44   --     3.38      0        0      1443                                    ______________________________________                                    

After addition of each test sample, no dust or gases were generated inany test and additional work could be conducted safely. When molten slagwas supplied to the slag pot, excellent diffusion and mixing wereobserved.

After allowing each slag to stand at room temperature for cooling afterbeing tested, the state of the slags were observed. Test Nos. 38 to 43showed no powdering or degradation.

After allowing these slag lumps to stand outdoors for three months, nochange was observed.

On the other hand, the conventional slag of test No. 44 to which no slagtreatment material was added decayed and powdered when it was cooled.

EXAMPLE 7 1 Preparation of a sample of slag treatment material

A material whose composition (weight) is as shown below was heated andsintered at a predetermined temperature for 20 minutes in an electricfurnace. After this sintering had been completed, the material heatedwas cooled below 100.C and crushed to prepare a slag treatment materialin which particles of from 0.1 to 0.5 mm comprised 90% or more of thematerial.

                                      TABLE 15                                    __________________________________________________________________________    Sample No. 37 38 39 40 41 42 43 44 45 46                                      __________________________________________________________________________    Boric acid anhydride                                                                           100      100   100   100                                     Borax anhydride                                                                          100                                                                              100   100                                                                              100         100                                        Colemanite(anhydride)                                                                              76                                                                               76   100                                              Rare lime  10.4  56.1      50                                                                               13                                                                               80                                                                               40                                        Magnesium oxide                                                                             5.1                      20                                     Quartz sand          30                30                                     Kaolin                 100                                                                              100       40                                        Sodium fluoride               39    40                                        Fluorite                         40    30                                     Calcining  700                                                                              700                                                                              400                                                                              700                                                                              700                                                                              400                                                                              650                                                                              400                                                                              650                                                                              500                                     Temperature                                                                   __________________________________________________________________________

The materials used were crushed as necessary, and the resultant particlesizes were adjusted to pass through a 16-mesh Tyler reference screen andfit in a 100-mesh screen. As a result, the mixed starting materialsshown in Table 15 were prepared to be used as the material for thesintering test. The chemical composition (weight %) of each slagtreatment material was as follows:

                                      TABLE 16                                    __________________________________________________________________________    Boric              Quick                                                                             Magnesium                                                                           Quartz  Sodium                                   acid     Borax                                                                             Colemanite                                                                          lime                                                                              oxide sand                                                                              Kaolin                                                                            fluoride                                                                           Fluorite                            __________________________________________________________________________    B.sub.2 O.sub.3                                                                    99.8                                                                              69.2                                                                              60.8                                                             Na.sub.2 O                                                                             30.8                        73.8                                     CaO          33.8  96                     57                                  MgO                    98                                                     Al.sub.2 O.sub.3                 44.2     0.5                                 SiO.sub.2     5.4            98  54.8     12                                  F                                    45.6 36                                  Residue       2.7  2                      6.7                                 Ig loss            2    2     2  1        3                                   __________________________________________________________________________

Colemanite was made a test sample after it had been completelydehydrated at 600° C.

The compositions of the thus-obtained slag treatment materials were asshown in Table 17, they being strong sintered material.

                  TABLE 17                                                        ______________________________________                                        Composition (wt %)                                                            Sample                                          Resi-                         No.   B.sub.2 O.sub.3                                                                      Na.sub.2 O                                                                            CaO  MgO   Al.sub.2 O.sub.3                                                                    SiO.sub.2                                                                          F    due                           ______________________________________                                        37    63     28      9                                                        38    66     29           5                                                   39    65             35                                                       40    56.1   15.1    12.3             16.4                                    41    42.5   11.4    9.3        16.7  20.0                                    42    40.5           19.4       18.2  21.9                                    43    37.7   18.6    29.0             3.35 11.1                               44    45.6           45.5                  14.4 5                             45    30.5   26.6    17.3       8.0   9.5  8.0                                46    55.6           9.5  10.9        16.4 7.6                                ______________________________________                                    

2 Slag modification test

When slag having basicity (CaO/SiO₂ =2.11) which is the first moltenslag tapped from an electric furnace for manufacturing stainless steel(capacity: 30 tons) was removed from a ladle to a slag pot, 40 Kg ofeach of the above slag treatment material test samples weresimultaneously supplied in 5 Kg vinyl bags. Next, after thethus-supplied slag was solidified by allowing it to stand at lowtemperature, the state of the slags were observed until the temperaturereached room temperature.

The test conditions are as follows:

                  TABLE 18                                                        ______________________________________                                                                       B.sub.2 O.sub.3                                     Sam-   Amount of Amount of                                                                              contained                                                                            Temperature                             Test ple    tapping   sample added                                                                           in slag                                                                              at tapping                              No.  No.    (t)       (kg/t slag)                                                                            (wt %) (°C.)                            ______________________________________                                        45   37     4.85      8.25     0.52   1412                                    46   38     5.39      7.42     0.49   1437                                    47   39     5.20      7.69     0.50   1429                                    48   40     4.88      8.20     0.46   1442                                    49   41     3.62      11.06    0.47   1437                                    50   42     3.18      12.59    0.51   1441                                    51   43     3.02      13.26    0.50   1423                                    52   44     4.15      9.65     0.44   1416                                    53   45     2.65      15.08    0.46   1429                                    54   46     4.54      8.81     0.49   1428                                    55   --     --        --       --     1435                                    ______________________________________                                    

After addition of each test sample, no dust or gases were generated inany test, and additional work could be conducted safely. When moltenslag was supplied to the slag pot, excellent diffusion and mixing wereobserved.

After allowing each slag to stand at room temperature for cooling afterbeing tested, the state of the slags were observed. Test Nos. 45 to 54showed no powdering or degradation.

After allowing these slag lumps to stand outdoor for three months, nochange was observed.

On the other hand the conventional slag of test No. 55 to which no slagtreatment material was added decayed and powdered when it was cooled.

Analyzed values of the slag for test (weight %) were as follows:

    ______________________________________                                        Test No. CaO      SiO.sub.2  MgO    Al.sub.2 O.sub.3                          ______________________________________                                        45 to 55 49 to 56 22 to 26   10 to 13                                                                             11 to 12                                  ______________________________________                                    

EXAMPLE 8

A predetermined amount of slag treatment sample 9 identical to that usedin Example 1 was added as packed in plastics film bags to fused slagoccurring during tapping from an electric furnace when the slag wasbeing removed from a ladle to a slag pot. After treatment, The slag wasmade into ballast by adjusting its particle size to a range equivalentto MS-25 after normal cooling by standing.

The presence of yellowish turbid water from the ballast was measured inaccordance with the following evaluation method. The results ofmeasurement and the chemical composition (weight %) are shown in Table19.

                  TABLE 19                                                        ______________________________________                                        Test No.     56      57      58    59    60                                   ______________________________________                                        Amount of slag                                                                             3.0     3.0     3.0   3.0   3.0                                  (t/ch)                                                                        Amount of addition                                                                         --      5       10    15    25                                   (kg/ch)                                                                       Rate of                                                                       addition                                                                      wt %         0       0.17    0.34  0.50  0.83                                 Conversion by B.sub.2 O.sub.3                                                              0       0.11    0.21  0.32  0.52                                 Chemical composition                                                          of slag (wt %)                                                                CaO          27.1    26.5    27.1  24.3  25.6                                 SiO.sub.2    20.6    20.2    20.5  21.1  20.3                                 MgO          15.6    11.0    16.8  15.4  19.7                                 Al.sub.2 O.sub.3                                                                           28.5    27.3    25.7  25.4  26.1                                 MnO          1.2     1.2     1.1   0.8   1.3                                  TiO.sub.2    0.7     0.8     0.5   0.5   0.6                                  FeO          2.2     0.9     2.6   1.1   2.3                                  S            1.9     2.2     2.3   2.6   2.0                                  P            0.005   0.005   0.005 0.005 0.005                                Color Identification                                                                       5.0     0.5     0     0     0                                    Test (yellow index)                                                           Remarks      Cont.   Comp.   E     E     E                                    ______________________________________                                         (Cont: Contrast example, Comp: Comparison example, E: Example)           

Method of evaluating yellowish turbid water

The thus-obtained 500 g of sample ballast was weighed, placed in 1500 mlof pure water, and boiled for 45 minutes in accordance with a coloridentification test per JIS A5015. The filtered eluate was put in acolor comparing tube so as to be visually tested with reference to apotassium bichromate color reference liquid upon the presence of color.In order to numerize the degree of darkness or lightness of the color ofthe eluate, that is the degree of the hue of the eluate, the absorbanceof the reference liquid and the eluate were measured with aspectraphotometer. The results were evaluated with the thus obtainedyellow index as shown in Table 20.

                  TABLE 20                                                        ______________________________________                                                                     Concentration of                                          Yellow   Absorbance potassium bichromate                             Hue      Index    (-log T)   reference (g/l)                                  ______________________________________                                        colorless                                                                              0        0.022 or less                                                                            0.002 or less                                    almost   0.5      0.022 to 0.064                                                                           0.002 to 0.006                                   colorless                                                                     extremely                                                                              1.0      0.064 to 0.113                                                                           0.006 to 0.011                                   light yellow                                                                  very light                                                                             1.5      0.113 to 0.181                                                                           0.011 to 0.018                                   yellow                                                                        slightly 2.0      0.181 to 0.30                                                                            0.018 to 0.032                                   light yellow                                                                  light yellow                                                                           2.5      0.30 to 0.46                                                                             0.032 to 0.052                                   yellow   3.0      0.46 to 0.80                                                                             0.052 to 0.10                                    slightly 3.5      0.80 to 1.02                                                                             0.10 to 0.17                                     dark yellow                                                                   dark yellow                                                                            4.0      1.02 to 1.09                                                                             0.17 to 0.30                                     very dark                                                                              4.5      1.09 to 1.16                                                                             0.30 to 0.45                                     yellow                                                                        brown    5.0      1.16 or more                                                                             0.45 or more                                     ______________________________________                                    

EXAMPLE 9

Each of slag treatment materials Sample Nos. 1, 3, 12, 15, 18, 25, 26,27, 28, 29, 30 and 40, each being packed in plastics film bags wereadded to a fused slag tapped from an electric furnace to comprise 0.40wt % B₂ O₃ at the time of being taken out from a ladle to a slag pot.After treatment the respective slags were made into ballast by adjustingparticle size to range corresponding to MS-25 after normal cooling bystanding.

The ballasts thus-obtained for each treatment material were tested forthe generation of yellowish turbid water similar to the abovedescription, with none of them generating yellowish turbid water.

Effect of the Invention

1 Since the slag treatment material according to the present inventioncomprises coarsely crushed substantially dehydrated heat treatedmaterial, especially, vitrified material, it will not generate degassingreactions such as degassing carbon dioxide gas or steam. As a result ofthis, working environments will not be deteriorated due to blowing orsplashing.

2 For similar reasons, there is substantially endothermic heat arisingfrom the fusion of the material heat of vaporation, heat of transitionetc. Therefore, the coarsely crushed vitrified material ca be quicklymelted into molten slag.

3 Diffusion after being melted into molten slag can be optionallyadjusted by using a supplement.

4 The slag treatment material according to the present invention canprevent slag powdering during cooling and substantially preventgeneration of yellowish turbid water.

5 The method according to the present invention is very advantageousfrom a industrial viewpoint since the slag treatment material can besupplied as it is packed in such as a polyvinyl chloride or polyethyleneresin bag, that is so-called polybags without requiring any changes inconventional processes.

What is claimed is:
 1. A slag treatment material comprising a materialfor improving molten slag in such a manner that the resulting fused slagis made resistant against powdering in a cooling process or againstgeneration of yellowish turbid water which is caused when said slag iscontacted with rain water, characterized in that: said slag treatmentmaterial is formed by coarsely crushing a substantially dehydrated heattreated material containing boron, having a particulate sizedistribution ranged from 0.1 mm to a first sized mass and melting pointbelow 1,100° C., wherein 90 wt % or more of the particles fall within arange of from 0.1 to 50 mm, and having a melting or softening pointranging from 700° C. to 1050° C., said substantially dehydrated heattreated material being a vitrified material, sintered material or amixture thereof and consisting essentially of the following componentsrepresented by, as oxide form, B₂ O₃ :20 to 50 wt %, Me₂ ¹ O:3 to 20 wt%, Me² O:10 to 35 wt %, SiO₂ : 20 to 50 wt % (wherein Me¹ represents analkali metal and Me² represents alkaline earth metal); and the balance(unavoidable contaminants): 0 to 10 wt %;and that said material whenadded to a slag and made into a ballast having a range equivalent toMS-25 and eluated in accordance with JIS A5015, provide aspectorphotometric index of less than about 1.0.